Brad I highly suggest "Andersonville" by MacKinley Kantor. A truly remarkable (and at times gruesome) retelling of the story surrounding a notorious rebel prison in Georgia. Mostly real characters with stories extracted from prisoner memoirs.
Mb Fields jr I'd recommend Doctorow's "March", focusing on Sherman, giving a powerful examination of what the Civil War was all about.
Donna Read Coal Black Horse by Robert Olmstead. A bit gruesome but its war. Part of the adventure takes place in Gettysburg.